Research was carried out in 1976 on the high temperature creep behaviour of a series of alloys along the pseudo binary section NiAl--Ni.sub.2 TiAl or .beta.+.beta.'. It turned out that the .beta.+.beta.' alloys had very much higher creep resistance than either phase separately, though the .beta.' phase is more creep-resistant than .beta.. (P. R. Strutt et al., Met. Trans. 1976, (7a) 23, 31). However, all .beta./.beta.' alloys are known to be highly brittle, especially at low temperatures, so that their use in demanding environments such as turbines cannot be contemplated. This invention arises from the idea that the Ni.sub.3 Al .gamma.' phase might impart room temperature ductility without destroying high temperature creep resistance